1. Cross-Reference to Related Applications
The present application claims priority from Japanese Patent Application No. 2011-015219 filed on Jan. 27, 2011, the entire content of which is incorporated herein by reference.
2. Field of the Invention
The present invention relates to a vehicle headlamp including a plurality of lamp units, each having a semiconductor light emitting device, such as an LED, as a light source, to form a light distribution pattern by superimposing light beams from the lamp units.
3. Related Art
In recent years, vehicle headlamps using semiconductor light emitting devices as a light source are being proposed. Generally, the semiconductor light emitting devices are light emitting chips, such as light emitting diodes (LEDs), having a square light emitting surface.
From a viewpoint of safety, vehicle headlamps may be required to form a light distribution pattern with high accuracy. Such a light distribution pattern is formed by an optical system including optical members, for example, a reflector and a projection lens.
A related art vehicle headlamp forms a light distribution pattern (e.g., a low-beam light distribution pattern) by a combination of a plurality of focused-beam lamp units and a plurality of diffused-beam lamp units, each of the lamp units having a semiconductor light emitting device as a light source (see, e.g., JP 2005-141917 A). The focused-beam lamp units form a focused beam pattern by projecting a plurality of light source images of light emitting surfaces of their semiconductor light emitting devices in a forward direction from the headlamp. The diffused-beam lamp units form a diffused beam pattern by projecting a plurality of light source images of light emitting surfaces of their semiconductor light emitting devices in the forward direction from the headlamp.
The diffused beam pattern is wider than the focused beam pattern in the vertical direction. According to the related art vehicle headlamp, the horizontal light diffusion and the vertical light diffusion are both controlled by optical members, such as a reflector and a projection lens, to form the diffused beam pattern. This light distribution control is complex.
To form the focused beam pattern, the light source images are condensed toward a cutoff line of the pattern so as to form a hot zone. However, this may cause an unnecessary brightness below the hot zone, or a strong irregularity in light intensity.